1. Field of the Invention
The present invention relates to a sensing system and a sensing method. More specifically, the invention relates to a sensing system and a sensing method utilizing circularly polarized light.
2. Description of the Related Art
Optical sensors are used in various fields and an optical sensor which detects a change in light intensity when a person enters an area in front of a door is used in an automatic door sensor. In addition, a banknote counter embedded in a vending machine or the like determines sizes of banknotes or reads printed patterns of banknotes by using an optical sensor.
A system using polarized light is known in the related art as a sensing system using an optical sensor. In JP2008-58270A, for example, cracks on a silicon substrate are detected with a system of irradiating the silicon substrate with polarized infrared light through a first linear polarizing filter and receiving reflected light or transmitted light from the silicon substrate through a second linear polarizing filter. The light intensity which can be sensed decreases, when the reflected light or transmitted light of a portion without cracks is linearly polarized light and travels through the second linear polarizing filter, except for a case where specific conditions are satisfied, however, this technology is acquired by using a phenomenon that light which can be sensed is generated even when the reflected light or transmitted light on the portion with cracks travels through the second linear polarizing filter due to diffuse reflection. In JP2013-36888A, a technology utilizing circularly polarized light in the technology of JP2008-58270A is disclosed. Here, a first circular polarizing filter which is provided in a light path of a beam between a light source and a silicon substrate, and a second circular polarizing filter which is on an extended line of the light path of a beam and is arranged on the silicon substrate a side opposite to a side where the first circular polarizing filter is arranged, have opposite polarization directions.
JP2003-96850A discloses an automatic faucet device which senses the hand of a person or an object using infrared light and prevents erroneous sensing using first polarizing means for allowing transmission of a linear polarized light component of floodlit infrared light and second polarizing means for allowing transmission of a linear polarized light component of infrared light emitted. In this device, light beams transmitted through the first polarizing means and the second polarizing means are different polarized light components, so as to detect diffuse reflection components and sense a target object.